This invention relates generally to cargo transporting vehicles (hereinafter referred to as cargo vehicle(s)) and to crane devices and more particularly to a crane device installed in a cargo vehicle with a roof structure such as a boxcar.
In general, for loading cargo onto the cargo deck or cargo room aboard a cargo vehicle such as a freight car of a boxcar type, for example, or for unloading cargo previously loaded into the cargo room, a cargo handling machine such as a forklift is used. The fork of a forklift, however, can reach only slightly into the doorway of a freight car such as a boxcar, whereby handling and moving of cargo between a doorway and places in the freight car which cannot be reached by the fork, must be carried out by manual labor. This requires a long work time and many workers, resulting in inefficiency.
Another problem encountered in the use of a forklift is that it can be used in only places where it can enter and operate with a certain degree of freedom, whereby the cargo loading and unloading areas are also limited.
One measure leading to a solution of these problems is the installation of a cargo handling device or machine in the cargo vehicle. In the installation of such a cargo handling device in a cargo vehicle, particularly a boxcar, certain further problems are encountered.
Since the space in the cargo room of a cargo vehicle with a roof structure is small, the moving parts of the cargo handling device, which according to this invention is a crane device, are liable to contact or strike against the ceiling or walls of the boxcar cargo room. Consequently the operation of the crane device requires skill on the part of the operator. Errors in the operation giving rise to collision between the moving parts of the crane device and the body parts of the boxcar will cause damage to such moving parts and/or the body parts.
The crane device in almost all cases has a winch with a drum for winding and unwinding a length of wire rope to raise and lower a cargo hook which is connected directly or via a block to the wire rope, and from which articles of cargo are suspended. The wire rope is ordinarily provided with ample total length so that a number of winding turns will be left on the drum when the cargo hook has been lowered to its lowest position for normal operation. The inner end of the wire rope is ordinarily anchored to the drum, whereby, if the entire length of the wire rope is unwound under abnormal circumstances, and the drum is continuously rotated in the same direction, the drum will then wind up the wire rope. If the inner end of wire rope should become disconnected from the drum when its entire length has been thus unwound, an extremely dangerous condition will arise.
In order to avoid such a hazardous condition, it is the ordinary practice to stop the unwinding operation of the winch when 3 to 4 or more winding turns of the wire rope are still remaining on the drum. Heretofore, this procedure has been practiced by the winch operator on the basis of his visual perception, experience, and intuition. This practice, however, lacks accuracy and positiveness.